Base station antennas for wireless communication systems are used to transmit radio frequency (“RF”) signals to, and receive RF signals from, cellular. Base station antennas are directional devices that can concentrate the RF energy that is transmitted in certain directions (or received from those directions). The “gain” of a base station antenna in a given direction is a measure of the ability of the antenna to concentrate the RF energy in that particular direction. The “radiation pattern” of a base station antenna is compilation of the gain of the antenna across all different directions. The radiation pattern of a base station antenna is typically designed to service a pre-defined coverage area, which refers to a geographic region in which mobile users can communicate with the cellular network through the base station antenna. The base station antenna may be designed to have minimum gain levels throughout this pre-defined coverage area, and it is typically desirable that the base station antenna have much lower gain levels outside of the coverage area. Early base station antennas typically had a fixed radiation pattern, meaning that once a base station antenna was installed, its radiation pattern could not be changed unless a technician physically reconfigured the antenna. Unfortunately, such manual reconfiguration of base station antennas after deployment, which could become necessary due to changed environmental conditions or the installation of additional base stations, was typically difficult, expensive and time-consuming.
More recently, base station antennas have been deployed that have radiation patterns that can be reconfigured from a remote location. For example, base station antennas have been developed for which settings such as the down tilt angle, beam width and/or azimuth angle of the antenna can be reconfigured from a remote location by transmitting control signals to the antenna. Base station antennas that can have their down tilt or “elevation” angle changed from a remote location are typically referred to as remote electrical tilt (“RET”) antennas, although the term “RET antenna” is now also commonly used to cover antennas that can have their azimuth angle and/or beam width adjusted from a remote location. RET antennas allow wireless network operators to remotely adjust the radiation pattern of the antenna through the use of electro-mechanical actuators that may adjust phase shifters or other devices in the antenna to affect the radiation pattern of the antenna. Typically, the radiation pattern of a RET antenna is adjusted using actuators that are controlled via control signal specifications promulgated by the Antenna Interface Standards Group (“AISG”).
Base station antennas typically comprise a linear array or a two-dimensional array of radiating elements such as dipole or crossed dipole radiating elements. In order to change the down tilt angle of these antennas, a phase taper may be applied across the radiating elements, as is well understood by those of skill in the art. Such a phase taper may be applied by adjusting the settings on an adjustable phase shifter that is positioned along the RF transmission path between a radio and the individual radiating elements of the base station antenna. One known type of phase shifter is an electromechanical “wiper” phase shifter that includes a main printed circuit board and a “wiper” printed circuit board that may be rotated above the main printed circuit board. Such wiper phase shifters typically divide an input RF signal that is received at the main printed circuit board into a plurality of sub-components, and then capacitively couple at least some of these sub-components to the wiper printed circuit board. These sub-components of the RF signal may be capacitively coupled from the wiper printed circuit board back to the main printed circuit board along a plurality of arc-shaped traces, where each arc has a different diameter. Each end of each arc-shaped trace may be connected to a radiating element or to a sub-group of radiating elements. By physically rotating the wiper printed circuit board above the main printed circuit board, the location where the sub-components of the RF signal capacitively couple back to the main printed circuit board may be changed, which thus changes the path lengths from the phase shifter to the radiating elements. This change in the path lengths results in a change in the phase of the sub-components of the RF signal, and since the arcs have different radii, the change in phase experienced along each path differs. Typically, the phase taper is applied by applying positive phase shifts of various magnitudes (e.g., +1°, +2° and +3°) to some of the sub-components of the RF signal and by applying negative phase shifts of the same magnitudes (e.g., −1°, −2° and −3°) to additional of the sub-components of the RF signal. Thus, the above-described wiper phase shifters may be used to apply a phase taper to the sub-components of an RF signal that are applied to each radiating element (or sub-group of radiating elements). Exemplary phase shifters of this variety are discussed in U.S. Pat. No. 7,907,096 to Timofeev, the disclosure of which is hereby incorporated herein in its entirety. The wiper printed circuit board is typically moved using an electromechanical actuator such as a DC motor that is connected to the wiper printed circuit board via a mechanical linkage. These actuators are often referred to as RET actuators since they are used to apply the remote electronic down tilt.